The present disclosure relates to sampling point adjustment apparatus and method and a program, and in particular, to a sampling point adjustment apparatus and method and a program capable of suppressing echo with high arithmetic efficiency and high precision.
In the related art, an acoustic echo canceller has been used in, for example, equipment which includes both a microphone and a speaker, such as a speaker phone, a video conference system, or the sound operation of a television receiver provided with a sound recognition function. Such an acoustic echo canceller has been used to suppress sound generated in such a way that sound reproduced from a speaker is wrapped around the input of a microphone, that is, acoustic echo.
In the general acoustic echo canceller, the signal of the sound reproduced from the speaker is acquired as a reference signal within equipment and the waveform of the reference signal is deformed by a filter which simulates propagation characteristics from the speaker to the microphone. Further, the reference signal on which a filtering process is performed is subtracted from an input signal acquired from the microphone, and thus acoustic echo is suppressed (for example, refer to Yougi Iiguni, “Adaptive Signal Processing Algorithm”, Baifukan (2000)).
However, in the acoustic echo cancelling apparatus, it is necessary that the sampling interval between Analog to Digital (AD) conversion performed on the input signal and Digital to Analog (DA) conversion performed on the reference signal should be accurately synchronized. The reason for this is that, if the sampling interval between the AD conversion and the DA conversion is deviated, echo suppression performance is sharply deteriorated when the amount of deviation is large (for example, refer to E. Robledo-Arnuncio, T. S. Wada and B. H. Juang “On Dealing with Sampling Rate Mismatches in Blind Source Separation and Acoustic Echo Cancellation” Proc. WASPAA, 34/37 (2007)).
However, with the increasing complexity of recent electronic equipment, cases in which a single piece of equipment is provided with a plurality of oscillators therein increase. In such equipment, there is a case in which original oscillators for sampling clocks supplied to a microphone and a speaker are different from each other. In this case, even when the respective sampling clocks are adjusted to have the same sampling frequency, the sampling interval between the AD conversion and the DA conversion is deviated because of element errors, change in temperature, or the like.
Here, in the acoustic echo cancelling apparatus, a technology has been proposed which causes the sampling interval of a reference signal to match with the sampling interval of an input signal by measuring sampling interval deviation and performing sampling rate conversion (for example, refer to M. Pawig, G. Enzner and P. Vary “Adaptive Sampling Rate Correction for Acoustic Echo Control in Voice-Over-IP”). The technology is configured such that the measurement of the sampling interval deviation and the estimation of a filtering coefficient are performed at the same time.